The present invention relates to a telephone-call prohibit circuit for preventing a telephone set from being used without approval.
The advancement of present-day communication technology has made possible direct long distance calls to other countries through automatic telephone dialing. For this purpose telephone sets can be used without difficulties. However, if the telephone set is frequently used for long distance calls without notice, its subscriber may be subjected to an extremly high telephone charge. In general, the prior art central-office (or PBX) switching equipment has a device which automatically can prohibit long distance calls that do not have approval. However, this sort of device has been impractical to mount in a desk-type telephone set for home use. It would be desirable to have a telephone set which includes in it a telephone-call prohibit circuit and in which prohibited telephone call numbers can be easily changed by telephone subscribers.